It is known, for example for the scanning of pictures during television broadcast or for the coding and storing of information, from Swiss application No. CH-A-468 135 to scan the picture line by line. For this purpose a light beam is oscillatingly deviated by means of a pivotable mirror and moved across the picture, where the light beam is modulated and reflected so that the differences in brightness can be transformed into analog electrical signals.
An exemplary embodiment for the drive of such a mirror is described in U.S. Pat. No. 3,624,574. In it a soft iron bar is exposed to a polarizing magnetic field of two permanent magnets diametrically opposed to each other with respect to a pivotal axis. In the orthogonal direction to this magnetic field a controlling magnetic field, consisting of two also diametrically opposed magnetic coils, is provided. The soft iron bar, having its longitudinal axis along the pivot axis, is rigidly connected at one end with a torsion bar and carries the mirror for the beam deviation. The torsion bar, clamped on one end, determines the central position for the mirror, namely in its non-pivoted normal position or in a position slightly deflected by the polarizing magnetic field.
Such an arrangement has the disadvantage that an additional mass must be moved, whereby in this mass additional energy is taken from the drive and transformed into heat, namely by the torsional force. In addition to this, the torsion bar needs to have a minimal final length which provides sufficient deflection, or the mirror must be far enough away from the picture to be scanned so that because of this distance sufficient deflection can be obtained. Both are values by means of which a device can be disadvantageously increased in size.